Military and tactical operations require various ammunition types and various types of semi-automatic and fully automatic firearms. The firearms are also used in both normal and silenced modes of operation. The various types of ammunition develop a wide range of gas pressures when the gunpowder burns. When silencers (sound suppressors) are used, they create a back pressure within the operating system of the firearm. The ambient temperatures in which the firearms are used also create a variation in the pressures within the firearm as the firearm is operated. Given all the conditions that cause variations in the pressures within the firearm, there are a seemingly infinite number of pressure variations that can occur. When a firearm is designed, the average working conditions are determined in view of expected variations in pressure within the firearm and stresses and construction material strengths calculated.
When a firearm is used in a semi-automatic mode without a silencer or in an automatic mode without a silencer, the speed of operation (cyclic rate) of the firearm is not a factor considered to affect a soldier's safety although the sound signature is considered to be a significant factor that adversely affect a soldier's safety due to alerting the enemy to the soldier's position. When a firearm is are used in the semi-automatic mode with a silencer, the cyclic rate of the firearm operation is not considered to be a significant factor that adversely affects the soldier's safety because the firearm only fires once per trigger squeeze, however, the sound signature could be a critical (i.e., life and death) factor depending on the ambient conditions. When a firearm is used in the fully-automatic mode with a silencer, the cyclic rate of the firearm operation and the sound signature could be a critical (i.e., life and death) factor to the soldier's safety depending on ambient conditions. A problem that has existed since the advent of gas-operated firearms that are used with silencers has been the increase in cyclic rate due to the increased backpressure created by the silencer installed on the end of the barrel. The cyclic rate increase due to the additional back pressure adds additional stresses to the firearm beyond the designed average working conditions causing material failures and ammunition-loading failures as well as an increased sound signature, both of which may compromise the safety of a soldier using the firearm.
Another problem that exists is the increase in cyclic rate of the firearm used in the semi-automatic and fully-automatic modes, which occurs when the ammunition type changes for a given firearm. Different ammunition types develop different operating pressures. Firearm operating temperatures based on duration of operation and ambient temperatures also affect operating temperatures. A difference in operating pressure above the pressure for which the firearm was designed increases in cyclic rate of the firearm, which causes excessive stresses on the operating parts of the firearm, and may cause breakage of the operating parts and/or ammunition-loading failures. The problems caused by greater-than-design pressures and/or increase in cyclic rate and sound signature (when used with a silencer) can result in creating a life and death situation for a soldier and/or the soldier's team members.